1. Field of the Invention
The present invention relates to a planar lighting apparatus, especially to a planar LED lighting apparatus.
2. Description of the Related Art
Lighting is important to our daily life, and after Edison invented the light bulb, we have been in the need of lighting assemblies day and night. Current lighting assemblies mainly include incandescent light bulbs, fluorescent tubes, and compact fluorescent lamps. Compact fluorescent lamps are used to replace incandescent light bulbs to provide compatible luminance in same operation manner. Fluorescent tubes are popularly used in offices or public places of large area. As illustrated in FIG. 1, a housing 10 has four fluorescent tubes 20 inside. The fluorescent tube 20 emits light uniformly in all directions. To increase light traveling to a light output face at the bottom side of the housing 10, three reflective bodies 12 are installed in the housing 10 with each of them placed between two adjacent ones of the four fluorescent tubes 20. The light output face is equipped with an anti-dazzle grille 16 or a lampshade.
For the present, environmental protection issues of power saving, low carbon consumption, and products without mercury are highly concerned, and LEDs (light emitting diodes) happen to meet the mentioned requirements. Besides, as LEDs are solid state devices, unlike traditional fluorescent tubes made of fragile glass, therefore they are far more convenient for transportation than traditional fluorescent tubes. In addition, LEDs have the advantages of small size and directional lighting, so they are suitable to be applied in lighting applications requiring small size or directional lighting, and are therefore becoming the main choice of next generation lighting in replacing traditional fluorescent tubes.
Please refer to FIG. 2, which illustrates a cross sectional view of a prior art planar lighting apparatus using LEDs. The apparatus has a housing 10, which includes a plurality of LEDs 22, and an anti-dazzle grille 16 or a lampshade on a light output face.
Although the small size of LEDs have the advantage of being capable of reducing the thickness of a lighting apparatus, however, the small size can also make the light intensity in a unit area so high as to result in a dazzling effect. To reduce the dazzling effect, one solution is to utilize a frosted lampshade to diffuse the light rays emitted from each LED. However, the intensity of output light will be attenuated accordingly. Besides, the light emitting efficiency of LEDs has been increasing per year as the manufacturing process keeps improving, and the increased light intensity has added challenges to the diffusion effect of the frosted lampshade. Under this circumstance, the frosted lampshade has to increase scattering effect to make the output light uniform, but this will further sacrifice the intensity of the output light.
In view of the mentioned problems, the present invention proposes a planar LED lighting apparatus, which is not only capable of reducing the thickness of the lighting apparatus, but capable of using a less frosted lampshade, or even using no lampshade, to provide a uniform planar lighting.